Impossible
by scrub456
Summary: Somehow, by some impossibility, the universe had apparently fractured. It was the only explanation for how John Watson had both kissed him and not kissed him. Twice. Schrödinger's kiss, his mind supplied unhelpfully. **this is a Towel Day prompt. A ridiculous, slightly OOC, case of mistaken identity resulting in friends to kissing for science. Also, it's never twins. Until it is.*


***A/N***

 _"There is no point in using the word 'impossible' to describe something that has clearly happened."_ ― Douglas Adams,Douglas, Dirk Gently's Holistic Detective Agency

* * *

Sherlock hadn't thought it was possible.

And that was the greatest error of all, wasn't it?

He knew, _knew,_ better than to underestimate his flatmate. John, consistent in a great many things, chief among them his continued ability to surprise Sherlock.

What Sherlock couldn't figure out was how John had succeeded in this deception for so long in Sherlock's own home.

While for most people, splitting the rent at Baker Street for mere months might qualify them as acquaintances, what Sherlock had with John was different.

Sherlock knew John. Trusted him implicitly. John had somehow become essential. Not just to the work, but in how Sherlock interpreted the world, how he fit into the flow of life around him.

He'd thought John felt the same.

So what if, in his misguided need to contribute to the household, John insisted on the farce that was maintaining locum work. Fine. If it helped John's sense of worth, Sherlock couldn't deny him. Less agreeable was John's distraction with insipid, tedious women. Though, Sherlock could hardly blame John for that either, after that mortifying conversation their first night as flatmates.

Sherlock allowed himself a moment to recall John's open, guileless face. The way his own mind ground to a screeching halt as he tried to calculate the potential. And how his mouth, his _damned_ traitorous mouth, had shut the whole thing down before it even had a chance to start.

And now this. It was Sherlock's own fault.

He shook his head in an attempt to clear his mind, pulled his collar up more securely to his chin, and huddled more deeply in the shadows under his umbrella.

* * *

It had started two weeks before with a case. Not even a case yet. Rumors and rumblings. The homeless network was ill at ease. Sherlock had waited for a night John had an overnight shift, then gone on a reconnaissance mission. Not looking for leads so much as testing the waters.

He hadn't been looking for anything specific when the most specific kind of surprise found him. He'd been waiting in a queue outside a club when two very inebriated men, their attention, and hands, focused only on each other, bumped him. A simple brush of the shoulder. Without turning back, a familiar, if slurred and gruff with exertion, voice mumbled, "S'rry mate."

"John?" Sherlock called after the familiar form. He stepped out of line to follow, but the two men, one with silver blond hair Sherlock would recognize under any circumstance, tumbled laughing into a cab and sped off into the night.

Sherlock had run all the way home, crashing through the flat in search of his friend, only to find himself alone. He'd stayed up all night, still in his coat, perched in his chair. Ready. Waiting to pounce.

When John finally returned, he looked haggard. Exhausted. Rumpled. He toed off his shoes, dropped his coat and work bag in his chair, and stood in the middle of the room as if he were lost. Sherlock cleared his throat, and John jumped.

"Christ, Sherlock. Don't…" He rubbed his eyes and they stared at each other a moment. "Have you slept?"

"I could ask you the same." Sherlock stood suddenly and stalked closer to John. He inhaled deeply… and smelled only antiseptic and tea. Clever.

"Of course I haven't."

" _Of course_ ," Sherlock mocked

"It's been a while since I've attempted an all nighter. 'M out of practice." John yawned.

"Can't have that, hmm, John?" Walking a tight circle around John, Sherlock's mind raced with the implications.

"What? That's… What is happening? I…" John pressed his fingers to his eyes. "Not that I'm not interested in whatever… _This_ is…" In a surprisingly agile move, he ducked away from Sherlock and headed toward his room. "I'm knackered. Don't even think about waking me for at least six hours." He turned then and disappeared up the stairs.

John never brought it up. Sherlock brooded, biding his time.

* * *

Sherlock had made the obvious decision to abandon his original cause in favor of stalking his flatmate. To think, he'd believed John incapable of deception. But another overnight shift, and two dates with someone John referred to as "Sarah," and Sherlock had all the evidence he needed. He'd caught glimpses, fleeting at best, of John at a different club each of those three nights. There was at least one other man beside the one that first night.

Sherlock didn't like the idea of John out with those other men, he refused to think too deeply about why. But more than that, he _hated_ the fact that John had lied to him, had kept this hidden from him. What was worse, he couldn't even really blame John for shying away from him.

He watched John enter the pub across the street, a mild venue by comparison, and waited for him to get settled at the bar with a drink. Shaking out his umbrella, Sherlock entered the pub behind a rowdy group of university students and tried to stay out of John's line of sight long enough to read the situation.

John had changed his clothes. He wore a tight grey t-shirt, and dirty, torn denims with boots. His hair was combed back in an effort to look casually tousled, but in reality far more styled than his normal. Sherlock wasn't sure what look John was going for, but he couldn't deny its effectiveness.

And it was obvious Sherlock wasn't the only one who noticed. The room seemed full of people who were taking note and making plans.

With a growl, he abandoned his umbrella on a passing drink tray, folded his collar down, ran his fingers through his hair, and stalked to the bar with his coat billowing behind him.

"I don't know what this game is you're playing," Sherlock pressed against John's back and let his voice rumble low against his ear. "But you had to know I'd figure it out."

John went rigid for only a moment, then swiveled on his seat to face Sherlock. In one quick movement he wrapped a hand around Sherlock's neck and pulled him into a deep, searing kiss.

Ideally Sherlock would have catalogued every finite detail for later review. John's technique. Every sensation. Sound frequency. The bloody atmospheric pressure. Everything. Instead, his mind once more ground to a halt. His eyes almost immediately drifted closed. One hand found John's right bicep, the other his left shoulder. And his damned traitorous mouth once again betrayed him by letting it happen.

John broke the kiss, panting against Sherlock's cheek. "Well. Hullo to you too, beautiful."

To his own mortification, Sherlock made an undignified noise. He refused to open his eyes. It was apparently all the invitation John needed to kiss him again.

Slowly, _too damn slowly,_ Sherlock's mind processes started to come back on line. _Well. Hullo to you too, beautiful_ echoed on a continuous loop. John had never called him that. It felt foreign. Off. The intonation was wrong. The speech pattern lazy. There was something… _Something…_

His mind couldn't make the connections with John's tongue in his mouth. He forced himself to counter the attack, his confidence bolstered when John made his own undignified noise. It was enough to draw attention to the fact that John tasted like rum (did John drink rum?) and cinnamon (he knew for a fact John did not care for cinnamon), and cigarettes (wrong, _wrong_!). There was a tiny flaw in the top left incisor Sherlock didn't remember ever seeing.

Suddenly his mind whirred back to full speed, and he was inundated with data. John had reached for him with his right hand, not his dominant left. The callouses on the fingers pressed to the back of his neck were all wrong, too rough, and the placement was off. Instead of antiseptic and tea, Sherlock was overcome by cheap cologne (too cheap even for John's thrifty tendencies), machine oil ( _that_ was… intriguing), and cigarettes ( _WRONG!_ ). Under the palm resting on John's left shoulder Sherlock could feel the smooth strain of the muscles, which very nearly caused another shut down, until he realized he wasn't feeling the thick spider web of a scar. Sherlock still couldn't bring himself to open his eyes.

Nothing was adding up. There was too much data. Also, not nearly enough data.

And then the impossible happened.

Again.

Just to his right someone cleared their throat. A warm, familiar presence of a particular height and build. And that presence spoke with a voice Sherlock knew well, this time with the correct intonation and precise speech pattern.

"Sherlock, what the hell?"

With a gasp Sherlock broke the kiss. John's kiss. But… John was asking him a question, and he sounded angry. Not angry. Confused. Hurt. Hurt? Yes. And jealous. Why jealous?

Wait. _Wait._ John couldn't be kissing him _and_ asking him questions.

"Sherlock? You okay?" And now John sounded worried. "Look at me."

Sherlock shook his head. He couldn't open his eyes. He _couldn't._

"Oi. Think I broke 'em," the John still gripping his neck laughed. And that was wrong too.

"Oh, fuck you. Give him some space." Gentle hands, _familiar_ hands, pushed the rough ones away.

And still Sherlock's mind raced. A true conundrum. A proper mystery. Somehow, by some impossibility, the universe had apparently fractured. It was the only explanation for how John Watson had both kissed him and not kissed him. _Twice._

 _Schrödinger's kiss_ , his mind supplied unhelpfully. He laughed and realized just how manic he must sound.

Gentle fingers, the fingers of John's left hand, brushed against the pulse point of his neck. "C'mon, Sherlock. Please open your eyes."

He couldn't do it. He didn't _want_ to do it. As long as his eyes were still closed there remained a version of reality where John had kissed him. There were plenty of people who lived fulfilling lives despite being blind. He could make it work. He shook his head.

One John laughed, the other cursed. The sweary one leaned in and whispered, "I didn't think you…" he sighed and pressed a soft kiss to his lips. He tasted of peppermint and tea and the chips from that place Sherlock preferred.

"Cor, Davey," an unknown voice boomed. "You make a move on Johnny's bloke? Bad luck, that. He's kicked yer arse for far less."

 _Davey?_ Sherlock did open his eyes then, and regretted it immediately. Surely He'd suffered some mind altering brain trauma. It was the only explanation for seeing two Johns standing in front of him. Two identical… No, not… Mirror images. Oh god. Oh _fuck._

"It's not… This is impossible. You. No. It's never…" Sherlock growled in frustration.

"Sometimes it actually is twins," John, the real John, shrugged. He looked almost ashamed. "You never… You didn't ask and you didn't deduce it, so I wanted to see how long it would take."

"Twins?" To his chagrin, Sherlock barely managed that much response. It was all too much.

"Wait, this is him, Johnny? This is your detective?" _Davey_ looked him up and down and stuck out his hand. "Since Johhny here's forgotten his manners, I'm David, his older brother."

"By three minutes," John grumbled. Sherlock just stared, unblinking, unmoving, at them.

"I have to say, mate, that mouth. Sinful." David winked. He _winked_. "Oh, dammit Johnny." He rubbed his arm where John had punched him.

"You and I? We'll talk later." John glared at David, who made an obscene gesture in return, before he guided Sherlock outside to hail a cab.

"So, twins." Sherlock thought he might actually go into shock. "It's never twins."

"Sorry to skew the data," John chuckled. He opened the car door for Sherlock and then climbed in after him. "What can I say? That's David, bane of my existence. Works construction. Looks like me. Less charming. Nowhere near as clever. Arse."

"He's a good kisser." Damned traitorous mouth. Sherlock buried his face in his hands.

John laughed outright at that. "To be fair, he had more time. Given the proper parameters…"

"Ilikedit," Sherlock murmured.

 _"What?"_

Sherlock exhaled deeply and turned in his seat to face John. "Your kiss. I liked it. Better. _Would very much like to…_ "

"Collect more data? Do a comparison?" John was laughing, but it wasn't malicious.

"No. Not a comparison, not an experiment, just…"

"A kiss?"

John's open, guileless expression was back, and Sherlock was lost. "How could I not see?"

"See what?" John whispered.

"You." Before he could think about it too much, he leaned in and kissed John. And John, perfect, brilliant, _impossible_ John, kissed him back, sending Sherlock's mind, once more, careening to a screeching halt. And for once, he couldn't be arsed to care.


End file.
